On Sun, 2008-09-28 at 18:56 +0100, David Woodhouse wrote:
> On Fri, 2008-09-26 at 13:46 -0700, David Woodhouse wrote:
> > At the worst, I should be able to reverse-engineer the library I
> have.
>
> The first failure seems to have been a discrepancy in epoch numbers.
And the others are due to patches which were committed to OpenSSL later
-- in particular, 'RFC4347 says HelloVerifyRequest resets Finished MAC',
which moves a call to ssl3_init_finished_mac(), and "Make DTLS1 record
layer MAC calculation RFC compliant", which sets the appropriate version
numbers in the packet in tls1_mac().
The full patch against 0.9.8e which makes this work (or at least
successfully negotiate and pass _some_ traffic -- I don't vouch for
later epoch changes) is below.
Next step would be to make it work in something newer. And preferably
with the RFC-defined version of the protocol instead of the old one.
Their client does seem to respond with the 'real' DTLS1 version if we
try that instead of using DTLS1_BAD_VER. And it has a CCS header length
of only 1 byte its responses, so it really is doing something different
and not just parrotting the version number. But just taking 0.9.8f and
setting the epoch in dtls1_reset_seq_numbers() as in the patch below
isn't sufficient -- I get the same record mac failure that I started
with.
This time it's going to be a little harder to guess what variant of the
new protocol they're using, because I don't have any implementation of
that -- and I'm not even sure it's _working_ on the server side. So I
suspect my best course of action now would be to somehow make it
possible to use the older version of DTLS in a current OpenSSL, for
compatibility? It's likely to be the only thing that's _tested_ against
Cisco servers anyway.
Index: ssl/d1_clnt.c
===================================================================
RCS file: /home/dwmw2/openssl-cvs/openssl/ssl/d1_clnt.c,v
retrieving revision 1.3.2.6
diff -u -p -r1.3.2.6 d1_clnt.c
--- ssl/d1_clnt.c 5 Dec 2005 17:32:19 -0000 1.3.2.6
+++ ssl/d1_clnt.c 28 Sep 2008 23:49:54 -0000
@@ -214,8 +214,6 @@ int dtls1_connect(SSL *s)
/* don't push the buffering BIO quite yet */
- ssl3_init_finished_mac(s);
-
s->state=SSL3_ST_CW_CLNT_HELLO_A;
s->ctx->stats.sess_connect++;
s->init_num=0;
@@ -225,6 +223,10 @@ int dtls1_connect(SSL *s)
case SSL3_ST_CW_CLNT_HELLO_B:
s->shutdown=0;
+
+ /* HelloVerifyRequest resets Finished MAC */
+ ssl3_init_finished_mac(s);
+
ret=dtls1_client_hello(s);
if (ret <= 0) goto end;
Index: ssl/d1_pkt.c
===================================================================
RCS file: /home/dwmw2/openssl-cvs/openssl/ssl/d1_pkt.c,v
retrieving revision 1.4.2.5
diff -u -p -r1.4.2.5 d1_pkt.c
--- ssl/d1_pkt.c 29 Nov 2006 14:45:13 -0000 1.4.2.5
+++ ssl/d1_pkt.c 28 Sep 2008 23:53:18 -0000
@@ -1718,12 +1718,12 @@ dtls1_reset_seq_numbers(SSL *s, int rw)
{
unsigned char *seq;
unsigned int seq_bytes = sizeof(s->s3->read_sequence);
+ int epoch;
if ( rw & SSL3_CC_READ)
{
seq = s->s3->read_sequence;
- s->d1->r_epoch++;
-
+ epoch = ++s->d1->r_epoch;
pq_64bit_assign(&(s->d1->bitmap.map),
&(s->d1->next_bitmap.map));
s->d1->bitmap.length = s->d1->next_bitmap.length;
pq_64bit_assign(&(s->d1->bitmap.max_seq_num),
@@ -1738,10 +1738,11 @@ dtls1_reset_seq_numbers(SSL *s, int rw)
else
{
seq = s->s3->write_sequence;
- s->d1->w_epoch++;
+ epoch = ++s->d1->w_epoch;
}
memset(seq, 0x00, seq_bytes);
+ s2n(epoch,seq);
}
#if PQ_64BIT_IS_INTEGER
Index: ssl/t1_enc.c
===================================================================
RCS file: /home/dwmw2/openssl-cvs/openssl/ssl/t1_enc.c,v
retrieving revision 1.35.2.3
diff -u -p -r1.35.2.3 t1_enc.c
--- ssl/t1_enc.c 16 Feb 2007 20:40:07 -0000 1.35.2.3
+++ ssl/t1_enc.c 28 Sep 2008 23:43:45 -0000
@@ -738,8 +738,8 @@ int tls1_mac(SSL *ssl, unsigned char *md
md_size=EVP_MD_size(hash);
buf[0]=rec->type;
- buf[1]=TLS1_VERSION_MAJOR;
- buf[2]=TLS1_VERSION_MINOR;
+ buf[1]=(unsigned char)(ssl->version >> 8);
+ buf[2]=(unsigned char)(ssl->version & 0xff);
buf[3]=rec->length>>8;
buf[4]=rec->length&0xff;
--
dwmw2
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